1. Field of the Invention
This invention relates to gas lift valves, and in particular, to a gas lift valve utilizing an extension spring biasing element.
2. Description of the Prior Art
It frequently occurs that hydrocarbon producing wells have insufficient pressure within the particular producing formation to naturally cause the hydrocarbons contained therewithin to flow upwardly toward the surface of the earth. In order to alleviate this condition and to economically extract the maximum available quantity of hydrocarbons from the particular producing formation, the gas lift technology has been developed.
With the gas lift technology pressurized gas is introduced into the interior of the production tubing string so that fluid present therein may be lifted to the surface to thereby reduce the pressure head of the fluid and permit the natural pressure of the producing formation to urge the desirable hydrocarbons into the well bore and toward the surface. In order to introduce the gaseous lifting fluid into the interior of the production tubing string, it is common in the art to dispose a plurality of gas lift valve assemblies on the exterior of the production tubing string to regulate and control the communication between the casing annulus surrounding the string and the interior of the production tubing string.
Each of the gas lift valve assemblies is particularly adjusted to open at a predetermined desired pressure, the pressure being related to the depth of the well at which the gas lift valve assembly is disposed. The pressure at which each gas lift valve assembly is opened is regulated in the prior art by either the presence of a predetermined pressurized fluid charge within an elastic and flexible bellows element or by the biasing force imparted to the valve by a compression spring. However, each of these methods has disadvantages. For example, if a pressurized bellows is used to impart the desired biasing force to the valve assembly, it is possible that temperature effects may alter the desired set point when the valve assembly is within its operating environment within the hydrocarbon producing well. Alternatively, if a compression spring element is utilized, it commonly occurs that buckling effects are present whereby the biasing spring abrades either against the interior of the valve housing in which it is disposed or against a guide rod disposed centrally and axially through the spring element. In either case, the frictional forces attendant upon the abutment of the compression spring with another member deleteriously affects the operation of the valve assembly and makes the pressure at which that assembly will open uncertain. Further, buckling of the compression spring element and frictional contact with another member increases hystersis effects during the opening and closing cycle of the assembly and also adversely affects the spring rate thereof. The substance of such buckling imparted by compression spring biasing elements is to render uncertain the pressure at which individual gas lift valve assemblies will open and operate.
It would therefore be advantageous to provide a gas lift valve assembly which eliminates the deleterious effects attendant upon the provision of compression spring biasing elements within the gas lift valve assembly. It would also be advantageous to provide a gas lift valve assembly utilizing an extension spring biasing element to maintain a predictably accurate closing force upon the gas lift valve assembly. It would be of even further advantage to provide an extension spring biasing element which maintains the predetermined biasing force that is set within the valve before it is lowered into its operating environment in the production string.
It is also common practice in the art to dispose the compression spring biasing element in a position within the valve housing wherein the spring is exposed to the deleterious environment present within the well annulus. That is to say, the biasing spring element is usually disposed so as to be in the communication path between the exterior annulus within the well casing and the interior of the production tubing. When combined with the effects attendant upon the use of the compression spring discussed above, exposure of the spring to the deleterious environment within the operating well further detracts from the predictability and reliability of the opening and operating set point thereof.
It would be therefore advantageous to provide a gas lift valve assembly wherein an extension spring biasing element is disposed within an isolated position within the valve housing.
It is also common practice within the prior art to provide a valve seat member within the valve housing and to maintain the seat in position through the use of a snap-ring member or the like. However, such prior art valve assemblies using such a snap-ring technique to dispose the valve seat member within the housing introduces a further inaccuracy in the opening point of the valve assembly due to the movement of the valve seat when exposed to the environment in the operating well. Such movements are not predictable and not taken into account when the valve is set at its supposedly fixed opening pressure set point.
It would therefore be advantageous to provide a gas lift valve assembly utilizing a fixed seat member threadedly engaged within the valve housing to prevent displacements of the valve seat with respect to the casing when the gas lift assembly is disposed in its operating environment within a production well.
In the prior art machining inaccuracies may cause the valve element within the gas lift valve assembly to be misoriented or out of alignment with its associated valve seat. When the valve element is integrally fabricated as an element of the internal structures of the gas lift valve and directly coupled to the biasing members, such misalignments are harmful in that they necessarily introduce fluctuations into the opening pressure set point and also cause leakage through the valve. It is also common practice in the art to position a check valve either upstream or downstream of the valve closing element to prevent fluid flow between the production tubing string and the annular region when the combination of pressures is sufficient to cause the gas lift valve to assume the open position.
It is seen therefore that it would advantageous to provide a gas lift valve assembly having a floating valve element therein so that in the seated position the valve element is completely seated on its associated valve seat and thus any inaccuracies in the machining of the element or the casing do not generate further inaccuracies in the opening pressure set point or permit leakage through the valve. It is therefore advantageous to physically disconnect the valve element from the bellows sub so that the physically disconnected, floating valve element may act as a check valve to prevent a back flow by remaining seated even if the pressure of the fluid within the production tubing is sufficient to overcome the closing forces on the bellows sub and move the bellows sub to its open position.